This is the C-terminal domain of ClpB protein, referred to as the D2-small domain, and is a mixed alpha-beta structure. Compared with the D1-small domain (included in AAA, Pfam:PF00004) it lacks the long coiled-coil insertion, and instead of helix C4 contains a beta-strand (e3) that is part of a three stranded beta-pleated sheet. In Thermophilus the whole protein forms a hexamer with the D1-small and D2-small domains located on the outside of the hexamer, with the long coiled-coil being exposed on the surface. The D2-small domain is essential for oligomerisation, forming a tight interface with the D2-large domain of a neighbouring subunit and thereby providing enough binding energy to stabilise the functional assembly [1]. The domain is associated with two Clp_N, Pfam:PF02861, at the N-terminus as well as AAA, Pfam:PF00004 and AAA_2, Pfam:PF07724.
PFAM PF10431